<!-- 我们知道现在的很多H5的小游戏的开发都是基于canvas这个画布的，其实canvas之所以这么强大考的是他强大的API库的结果，知道一些canvas的基本API并且可以利用这些API是一个前端开发人员的基本素质，那么我们今天就来跟着小编来一起利用面向对象的思想来封装一个折线图的绘制

   html代码

   

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<canvas style="border:1px solid red" width="500" height="500"></canvas>  
    </body>  
<!-- JavaScript代码
   

[html] view plain copy -->
<script>  
    //获取canvas的dom元素  
    var cvs=document.querySelector("canvas");  
    //创建绘制环境  
    var cxt=cvs.getContext("2d");  
      /*  
        * constructor { LineChart } 折线图构造函数  
        * param { ctx: Context } 绘图上下文  
        * param { paddingArr: Array } 折线图到画布四边的距离，存储顺序为上右下左  
        * param { arrowArr: Array } 折线图中箭头的宽和高  
        * param { data: Array } 存储了折线图中所需的数据  
        * */  
        function LineChart(ctx,paddingArr,arrowArr,data){  
            this.ctx=ctx;  
            this.paddingArr=paddingArr;  
            this.arrowArr=arrowArr;  
            this.data=data;  
            this.arrowHeight=arrowArr[0];  
            this.arrowWidth=arrowArr[1];  
  
            //计算上顶点的距离  
            this.vertexTop={  
                x:this.paddingArr[3],  
                y:this.paddingArr[0]  
            };  
            //计算原点的距离  
            this.origin={  
                x:this.paddingArr[3],  
                y:this.ctx.canvas.height-this.paddingArr[2]  
            };  
            //计算右边点的距离  
            this.vertexRight={  
                x:this.ctx.canvas.width-this.paddingArr[1],  
                y:this.ctx.canvas.height-this.paddingArr[2]  
            };  
            this.process();  
        }  
  
        LineChart.prototype={  
            //设置构造函数  
            constructor:LineChart,  
            //绘制坐标轴中的两条线  
            drawZuobiao:function(){  
                this.ctx.beginPath();  
                this.ctx.moveTo(this.vertexTop.x, this.vertexTop.y);  
                this.ctx.lineTo(this.origin.x, this.origin.y);  
                this.ctx.lineTo(this.vertexRight.x, this.vertexRight.y);  
                this.ctx.stroke();  
            },  
            drawArrow:function(){  
                this.ctx.beginPath();  
                this.ctx.moveTo(this.vertexTop.x, this.vertexTop.y);  
                this.ctx.lineTo(this.vertexTop.x-this.arrowWidth/2, this.vertexTop.y+this.arrowHeight);  
                this.ctx.lineTo(this.vertexTop.x, this.vertexTop.y+this.arrowHeight/2);  
                this.ctx.lineTo(this.vertexTop.x+this.arrowWidth/2, this.vertexTop.y+this.arrowHeight);  
                this.ctx.closePath();  
                this.ctx.fill();  
                this.ctx.stroke();  
  
                this.ctx.beginPath();  
                this.ctx.moveTo(this.vertexRight.x, this.vertexRight.y);  
                this.ctx.lineTo(this.vertexRight.x-this.arrowHeight, this.vertexRight.y-this.arrowWidth/2);  
                this.ctx.lineTo(this.vertexRight.x-this.arrowHeight/2, this.vertexRight.y);  
                this.ctx.lineTo(this.vertexRight.x-this.arrowHeight, this.vertexRight.y+this.arrowWidth/2);  
                this.ctx.closePath();  
                this.ctx.fill();  
                this.ctx.stroke();  
  
            },  
  
            process:function(){  
                this.processData=[];  
                //在这一部分将画布认识的坐标转化为本坐标系的坐标  
                for (var i = 0; i < this.data.length; i+=2) {  
                    this.processData.push(this.origin.x+this.data[i]);  
                    this.processData.push(this.origin.y-this.data[i+1]);  
                };  
                  
            },  
  
            drawOrcle:function(){  
                this.ctx.beginPath();  
                for (var i = 0; i < this.processData.length; i+=2) {  
                    this.ctx.arc(this.processData[i],this.processData[i+1], 5, 0, Math.PI*2);  
                    this.ctx.fill();  
                      
                };  
            },  
  
            drawLine:function(){  
                this.ctx.beginPath();  
                for (var i = 0; i < this.processData.length; i+=2) {  
                    this.ctx.lineTo(this.processData[i], this.processData[i+1]);  
                };  
                this.ctx.stroke();  
  
            },  
            draw:function(){  
                this.drawZuobiao();  
                this.drawArrow();  
                this.drawOrcle();  
                this.drawLine();  
            }  
        };  
  
        var linechat=new LineChart(cxt,[20,20,20,20],[10,10],[10,10,20,20,60,60,100,100]);  
        linechat.draw();  
  
          
</script>  
    <!-- 具体的详细步骤已经在代码里有所体现了，放到H5标准下的页面就好了！
版权声明：本文为博主原创文章，未经博主允许不得转载。	https://blog.csdn.net/u0130354 -->